Several products are used in the building industry that utilize calcined gypsum, also known as stucco, plaster of Paris, or calcium sulfate hemihydrate. Calcined gypsum is the primary component of plaster. When water is added to calcined gypsum, it hydrates to form an interlocking matrix of calcium sulfate dihydrate, hardening to a solid mass.
Plaster is generally applied to a special substrate, such as lath, that holds the plaster in position as it sets and also is strong enough to hold the weight of the plaster applied to it. Plaster can also be applied as a veneer coating in a thin layer over wallboard. Special wallboard, known as “blue board,” is recommended for use with veneer plaster.
Veneer plaster is a calcined gypsum plaster which is specially formulated to provide specific workability, strength, hardness and abrasion-resistance characteristics when applied in thin coats ( 1/16″ nominal) over veneer gypsum base or other approved base.
Lime bucking, or simply bucking, is a condition associated with lime putty, veneer, and other plastering materials which is characterized by poor workability or stiffness well before normal setting. It is an early stiffening effect that takes place shortly after mixing the dry powdered product with water. When lime bucking occurs, the plaster mortar loses its ability to flow and becomes a highly viscous putty which often times is unusable as a trowelable material.
There is a need for methods of reversing lime bucking in plaster slurries. Furthermore, there is a need for plaster compositions which reduce or eliminate the occurrence of lime bucking when the plaster slurry is made.